An image forming apparatus of an electrophotographic system detects, in temperature control for a fixing device, the temperature of the outer circumferential surface of a heat roller in a non-contact manner using non-contact temperature detecting means and controls, with a control unit, the temperature to a predetermined fixing temperature.
It has been proposed to measure the surface temperature of the heat roller using an inexpensive non-contact thermistor instead of an expensive thermopile as the non-contact temperature detecting means (JP-A-2009-175538)
Compared with the thermopile, the non-contact thermistor causes deterioration in detection accuracy of temperature because of the influence of a gap between the non-contact thermistor and the heat roller surface, which is a measurement target, and ambient temperature. Therefore, in some cases, highly accurate temperature control cannot be performed. Further, it is likely that, depending on an attachment state of the non-contact thermistor, fluctuation occurs in the gap between the non-contact thermistor and the heat roller surface and the heat roller cannot be accurately controlled.